The present invention relates to an improved apparatus for tempering glass sheets and a method of tempering utilizing that apparatus.
Many methods of treating glass to cause it to break in small, harmless pieces, rather than large, elongated shards which can cause serious injury, have been practiced. The goal of early tempering methods to treat relatively small sheets of glass was to uniformly distribute the airflow over the entirety of the surface of the glass sheet. As single glass sheets used, for example, in vehicles became larger, and the analysis of stresses in glass became more sophisticated, methods of differentially treating areas of a glass sheet were devised. One particularly intractable problem has been the elimination of inadequately tempered areas, relatively near the center of large sheets of glass such as automotive backlights.
Thus, those skilled in the art of glass tempering have continued to search for a way to improve tempering, on a consistent basis, during time-critical automotive glass manufacturing operations.
As noted, glass tempering or heat treatment is the subject of many patents, for example:
U.S. Pat. No. 4,314,836 describes a construction and arrangement of a tempering medium supply system that is said to provide relatively wide escape paths in the direction of the glass sheet thickness for blasts of tempering medium applied toward the central portion of the glass sheet compared to the escape paths provided in said direction for blasts of tempering medium applied to the portion of the glass sheet beyond the central portion. The resulting tempered glass sheets utilizing the process of the present invention are said to produce fragments meeting code requirements in the central portion as well as the portion beyond the central portion when subjected to destructive testing.
U.S. Pat. No. 4,323,385 describes a process for uniformily tempering the entirety of a glass sheet utilizing plenum chambers having aperture walls facing the opposite major surfaces of the glass sheet, wherein the apertures are constructed and arranged to be smaller and more closely spaced in the portion of the plenum that faces the central portion of the glass sheet during tempering than the apertures provided in the wall outside the central portion. Nozzles extending from said apertures are constructed and arranged so that nozzles extending from the relatively small diameter, more closely spaced apertures of the central portion of the wall are longer, and narrower and have their ends closer to the major surface of the glass sheet than the relatively widely spaced nozzles of relatively larger cross-section that extend from the remaining apertures in the aperture wall.
U.S. Pat. No. 4,508,783 describes a method of differentiated rate of hardening of a glass sheet by blowing a cooling gas in the direction of the sheet having two zones, from nozzles. According to the invention, a simultaneous solidification of the glass sheet is said to be produced at both zones of the sheet in spite of the differentiated treatments applied to establish a difference of hardening between the different zones of the sheet.
U.S. Pat. No. 4,773,926 describes a tempering process for glass sheets of ±2mm in thickness in which process, a plurality of nozzles from which a gas flow emanates, are located so that their free ends are directed toward the glass sheet in a position spaced slightly apart from the glass surface. Each nozzle is pierced by a narrow, calibrated orifice and the feed pressure of each nozzle is maintained for purposes of blowing the gas, generally air, at least at sonic speed toward the surface of the sheet. The configuration of the nozzles are said to ensure that the speed of the blowing gas is, at least, at sonic speed at the surface of the glass sheet, thus optimizing coating power. One measure to increase the evacuation of the blown air is said to be accomplished by the use of nozzles having longer tubular bodies extending toward the free end. The nozzles may be longer in relation to the width of the tempering station. Additionally, or alternatively, the flow of blown air may be increased in volume per unit surface area.
U.S. Pat. No. 6,412,309 describes a glass quenching apparatus including a first nozzle group for jetting blower air onto opposite surfaces of the glass sheet, the first nozzle group being stationary nozzles, and a second nozzle group being movable nozzles for jetting compressor air onto at least one of the opposite surfaces of the glass sheet, which nozzles are capable of moving parallel to a plane of the glass sheet. The movable nozzle group can be located, it is said, at an optimum position with respect to, for example, a hard-to-cool portion of a glass sheet.